Mountain bicycle stem



FIG. 1 is an isometric view of a mountain bicycle stem embodying my newdesign;

FIG. 2 is a left side elevation view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a front elevation view thereof; and

FIG. 6 is a rear elevation view thereof.

The ornamental design for a mountain bicycle stem, as shown.